P22FD code meaning
NOx Sensor Performance - Slow Response High to Low (Bank 1 Sensor 2)
Powertrain system Generic code P22xx codes Check engine light
What P22FD means
P22FD stands for the falling edge at the rear NOx sensor on bank 1: after a NOx peak downstream of the SCR catalyst, the signal decays more slowly than permitted. No manufacturer documents this code publicly, and no bulletin in the NHTSA index names it. How such a check works is visible in GM's front-sensor test P22FA, which times the drop between two fractions of the starting value (on the 6.6L LML 2.3 s from 70 to 40 %), while GM itself puts rear-sensor dynamics into P229F. Engines with a third NOx sensor have P23C0 for the same fault at sensor 3. Section (f)(5.2.2)(A) of CARB's OBD II rule names response rate among the sensor faults to detect. A sluggish outlet sensor makes the SCR look weaker than it is and can lead to efficiency codes such as P20EE.
P22FD at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.3 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P22FD
- Check engine light on
- SCR efficiency code may appear as well
Common causes of P22FD
- Most likelyRear NOx sensor aged or coated, signal falls too slowly
- PossibleUrea crystals around the sensor tip after dosing faults
- Less likelyExhaust leak close to the outlet sensor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nox sensorSCR catalyst
What each part of P22FD means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 2 | Area: fuel and air metering (injector circuit). |
| FD | The exact fault in that area. |
What to do next
- Note P22FD and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P22FD
What does P22FD mean?
P22FD means "NOx Sensor Performance - Slow Response High to Low (Bank 1 Sensor 2)". P22FD stands for the falling edge at the rear NOx sensor on bank 1: after a NOx peak downstream of the SCR catalyst, the signal decays more slowly than permitted. It is a generic code, so it means the same on every make.
Is it safe to drive with P22FD?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P22FD fail an emissions test?
Yes, it can. P22FD is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P22FD to fix?
Difficulty: medium. A typical repair takes 0.3 to 2 hours of work. This is a job for a workshop.
Will P22FD clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.